Back spacing mechanism



6 Sheets-Sheet 1 Fi led May 23, 1966 .mm N

' INVENTOR filo-:1 W4? BY d J fl'M ATTORNEY July 15, 1969 H. SCHWEIZER3,455,430-v BACK SPACING MECHANISM Filed May 25, 1966 6 Sheets-Sheet 2INVENTOR WA,

BY w/ JiJk a/ ATTORNEY July 15, 1969 H. SCHWEIZER BACK SPACING MECHANISMFiled May 25, 1966 6 Sheets-Sheet 5 Fig.2!) 43 INVENTOR ATTORNEY I July15, 1969 H. SCHWEIZER 3,455,430

BACK SPACING MECHANISM Filed May 23, 1966 6 Sheets-Sheet 4 INVENTORATTORNEY y 15, 1959 H. SCHWEIZER 3,455,430

BACK SPACING MECHANISM Filed May 25, 1966 6 Sheets-Sheet 5 ATTORNEY July15, 1969 H, SCHWEIZER 3,455,430

BACK SPAC ING MECHANI SM Filed May 23, 1966 6 Sheets-Sheet 6 l UnitedStates Patent U.S. Cl. 19791 Claims ABSTRACT OF THE DISCLOSURE A set ofescapement pawls cooperates with the rack of a carriage to blockcarriage movement after steps of different length, and are connected bycoupling means to backspacing means which shift coupled pawls forwardand rearward, and into and out of recesses of the rack to obtainbackspacing of the carriage.

The present invention invention relates to a back spacing mechanism forthe escapement mechanism of a carriage, and more particularly tomechanism for moving the paper carriage of a typewriter in steps whichare proportional to the dimensions of the typed characters.

The escapement mechanism includes a set of escapement pawls, preferablythree pawls, which sequentially cooperate with the teeth and recesses ofa rack secured to the paper carriage. The escapement pawls are mountedon a stationary shaft for turning movement into and out of the recesses,and for longitudinal movement along the rack of the paper carriage. Eachpawl cooperates with two releasing members which, in accordance with theselected type character and corresponding step, release thecorresponding pawls so that only one pawl stops the carriage after astep of a desired length. Consequently, assuming that three escapementpawls are provided, the pawls have three different positions relative toeach other, one pawl enaging a blocking means to stop the carriage,while the other pawls are spaced distances corresponding to one and twosteps, respectively, from the stop means.

It is one object of the invention to combine a proportional escapementmechanism of this type with a back spacing device permitting thecorrection of errors by moving the paper carriage rearward.

Another object of the invention is to combine an escapement mechanismwhich permits the carriage to move steps of different length, with aback spacing de vice which back spaces the paper carriage for a distancecorresponding to the shortest step.

It is another object of the invention to provide a combined back spacingand escapement mechanism using the escapement pawls for the back spacingoperation.

With these objects in view, the present invention relates to a backspacing mechanism, and more particularly to a combined back spacing andescapement mechanism for a paper carriage which is movable forward in awriting direction and rearward in a back spacing and return direction.

One embodiment of the invention comprises a set of escapement pawls,preferably three pawls, cooperating with the teeth and recesses of therack of the carriage, and having stop portions staggered relative toeach other a predetermined distance in the direction of the carriagemovement; blocking means engage the stop portion of the leading pawl forblocking forward movement of the carriage while the stop portions of theother pawls are rearwardly spaced from the leading stop portion and fromthe blocking means; a set of coupling means respectively correlated withthe pawls and being individually 3,455,430 Patented July 15, 1969 andindependently movable between a position of rest, a first couplingposition coupled with the leading pawl which engages the blocking means,and a second coupling position coupled with another pawl, preferablywith the second trailing pawl; actuating means for moving the couplingmeans to the coupling positions, and for moving the coupling means inthe first coupling position together with the respective pawl rearwardso that the carriage is rearwardly moved and for moving the couplingmeans in the second coupling position forward so that the respectivepawl moves out of an engaged recess and forward relative to therearwardly moving rack and then engages the next leading recess whilethe stop portion thereof engages the blocking means for blocking forwardmovement of the carriage; and back spacing means for operating theactuating means.

The predetermined distance between the stopping portions of theescapement pawls, which corresponds to the minimum carriage step, is thedistance between adjacent recesses of the rack of the paper carriage,divided by the number of pawls in the set. The coupling means in thesecond coupling position engages the pawl whose stop portion trails theleading stop portion of the leading stop, two of these distances.

In the preferred embodiment of the invention, the actuating meansinclude biassing means for urging the coupling means whose associatedpawls are in the corresponding positions into the first and secondcoupling positions respectively, and a turnable drive means havingrearwardly and forwardly acting parts for moving the coupling means inthe first coupling position rearward, and the coupling means in thesecond coupling position for ward, respectively. The drive means has anormal position for holding the coupling means in the position of rest,and an actuating position for releasing the coupling means for movementunder the action of the biassing means to the first or second couplingpositions. Further turning of the drive means causes forward andrearward movement, respectively, of the coupling means in the couplingpositions with the respective pawls, to effect back spacing of thecarriage and blocking of the same after the step in rearward direction.The back spacing key is operatively connected with the drive means foroperating the same. 4

In the preferred embodiment of the invention, the several pawls havestaggered stepped recesses with staggered shoulders, which are engagedby the respective coupling means in accordance with the staggeredpositions of the pawls so that different shoulders of a stepped recessare engaged in the first and second coupling positions, causing arelative displacement between the respective coupling means in couplingpositions and the rearwardly and forwardly acting parts of the drivemeans. Consequently, only one pawl is shifted in forward writingdirection, and another pawl is shifted backward, while the remainingpawl or pawls are not actuated but follow the movement of the other pawlin backward direction.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawing, inwhich:

FIG. 1a is a fragmentary elevation, partially in section along line1a-1a in FIG. lb, illustrating an escapement mechanism combined with aback spacing mechamsm;

FIG. 1b is a fragmentary plan view of the embodiment of FIG. 1a;

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FIG. 2a is a fragmentary elevation, corresponding to FIG. 1a, butomitting parts of the same for the sake of simplicity, and illustratingthe mechanism in a first operational position in which the longest pawlblocks the can riage movement;

FIG. 2b is a plan view illustrating the mechanism in the position ofFIG. 2a;

FIG. 3a is a fragmentary elevation partly in section taken along line3a3a in FIG. 3b and corresponding to FIG. 2a, but illustrating themechanism in another operational position in which the shortest pawlblocks the carriage movement;

FIG. 3b is a fragmentary plan view illustrating the mechanism in theposition of FIG. 3a;

FIG. 4 is a fragmentary elevation illustrating on an enlarged scale, adetail of the mechanism in an operational position assumed between thepositions of FIG. 2a and FIG. 3a;

FIG. 5 is a fragmentary elevation illustrating on an enlarged scale adetail of the mechanism in another operational position in which theshortest pawl is operative to block carriage movement; and

FIG. 6 is a fragmentary elevation illustrating on an enlarged scale adetail of the mechanism in a further operational position in which apawl of intermediate length blocks the carriage movement.

Referring now to the drawing, and more particularly to FIGS. 1a and 1b,the paper carriage of a typewriter, not shown, carries the escapementrack 1, and is urged by the carriage spring, not shown, to move in aforward writing direction indicated by the arrow 2. During the carriagereturn or during a back spacing operation, the carriage with rack 1moves in the opposite rearward direction.

The teeth 3 of the rack 1 are spaced at distance t which is equal tothree smaller distances 0. An escapement mechanism P includes threepawls 4 whose engaging portions 5 cooperate with the recesses betweenteeth 3 of rack 1. The pawls 4 are operated in a manner which is not anobject of the invention, to permit the carriage to move steps ofdifferent length proportionate to the dimensions of a typed character,the steps having a length of one, two or three distances 2. FIGS. 1a andlb also show parts of a return mechanism R which is not an object of theinvention, and a back spacing mechanism S which, in accordance with theinvention, is combined with the escapement mechanism P. The set ofescapement pawls 4 is mounted on a stationary rod or shaft 7 for turningmovement into and out of the recesses between teeth 3, and for movementin the direction of rack 1 and of the carriage movement. Pawls 4 haveslots 6, open at one end, and closed at the other end by semicircularstop portions 6', which are spaced different dis tances L L L from thetip of the respective engaging portion 5, and since the pawls 4 are of acorresponding length, the foremost pawl 4 is the longest, and therearmost pawl 4 is the shortest. Distance L +e is distance L anddistance L, is distance L +e, as diagrammatically indicated in the upperportion of FIG. 1a. In the position of FIG. 1a, the longest pawl 4blocks movement of the carriage since its stop portion 6 abuts blockingshaft 7. Stop portion 6' of the intermediate pawl 4 is spaced thedistance :2 from the blocking shaft 7 and stop portion 6 of the rearmostpawl 4 is spaced the distance e from the stop portion 6 of theintermediate pawl 4 and a distance 2e from the blocking shaft 7.Consequently, the intermediate and rearmost pawls 4 do not blockcarriage movement in the position of FIG. la. The stop portions 6 havesubstantially the same diameter as shaft 7.

FIG. 1a shows the foremost longest pawl 4 in dash and dot lines and maybe considered as a section along line 1a1a in FIG. lb, with the foremostpawl 4 shown in phantom lines.

Each of the pawls 4 is biased by a spring 8 engaging an arm 9 to turn incounterclockwise direction about blocking shaft 7, and also to moverearward along the rack 1. The force of any spring 8 urges therespective pawl 4 to engage the rack 1 with its engaging portion 5.FIGS. 1a and 2:: show the engaging portions 5 of all three pawls 4located in the same recess between adjacent teeth 3' and 3", and sincethe carriage spring urges rack 1 in the direction of the arrow 2, theflank of tooth 3 urges all three pawls 4 towards the left, overcomingthe weaker springs 8, so that the longest pawl 4 abuts blocking shaft 7with its stop portion 6, while stop portions 6 of the shorter pawls 4are spaced from the blocking shaft 7. Only the foremost pawl 4 blocksmovement of the carriage. The staggered position of stop portions 61 isalso shown in FIGS. 2a and 212.

Each pawl 4 has a projecting lug 10, having a shoulder 10, and theshoulders 10' of the three pawls 4 are spaced predetermined distances 0from each other so that shoulders 10' are spaced the same distance fromstop portions 6' of the respective pawl 4. Shoulders 10' cooperate withengaging edges 11, '11'a of pairs of releasing members 11, 110, one pairof releasing members 11, 11;a being respectively associated with eachpawl 4. Releasing members 11, 11a have slots '12 open to the right asviewed in FIG. la, and embracing shaft 7 so that the releasing members11, 11a are guided for longitudinal and turning movement. Springs 13 and13:: are respectively connected with each pair of releasing members 11,11a and urge the same to turn in counterclockwise direction until a stop14- abuts a stationary abutment 15, schematically indicated in FIG. la,and preferably mounted on the frame 50 of the machine. The action ofsprings 13, 13a urges releasing members 11, 11a to the right until edges11', 11'a abut shoulders 10 of lugs 10 of. pawls 4.

Each releasing member 11, 11:: has a projecting portion 16, 16a.Projecting portions 16, 16a project over the respective lug 10 of theassociated pawl 4. Projecting portion 16 of each releasing member 11projects over the respective lug 10 substantially the distance 2 so thatwhen releasing member 11 turns in clockwise direction, engagement of lug10 is assured. Projecting portion 16a of each releasing member 11a is adistance 1 longer than projecting portion 16, the distance t being thespacing between adjacent teeth of rack 1. A locking member 48 with alocking portion 31 cooperating with locking teeth 30 in releasingmembers 11, 11a is biased by spring 49. Parts 11, 11a, 48 belong to anescapement mechanism P which is not an object of the present invention,and these parts have been shown and illustrated only for the sake ofcompleteness, and have no bearing on the present invention. It will beunderstood that pawls 4 can be operated under the control of thereleasing members 11, 11a and of the locking member 48 to release andengage the teeth of the rack 1 to cause stepwise movement of thecarriage under the action of the carriage spring, not shown, for stepswhose lengths are either e or 2e or 3e, depending on the width of thelast typed character.

The present invention is concerned with the use of the escapement pawls4 to obtain a back spacing of the carriage in steps having the length ofthe predetermined distance e which is one-third of the spacing t of twoteeth 3 of rack.

As also shown in FIGS. 2a to 6, each pawl 4 is provided in accordancewith the invention with a stepped recess bounded by a first couplingshoulder 44', a first abutment 44, another shoulder 45", a secondabutment 45, and a second coupling shoulder 45'. The stepped recessesare staggered the above-defined distance e relative to each other. Thedeeper portion 45a of each recess is bounded by edges 45, 45, 45" andthe shallower portion of each recess is bounded by edges 44 and 44. Therecesses cooperate with coupling portions 35 of a set of three couplinglevers 35 and a coupling portion 35 cooperates with the first couplingshoulder 44' of the associated pawl 4 to shift the same toward the rightfor moving the carriage in the back spacing direction, and cooperateswith a second coupling shoulder 45 of the associated pawl 4 for movingthe same in a forward direction while the engaging portion 5 of therespective pawl 4 moves forwardly into the next following recess as willbe described in greater detail hereinafter.

Coupling shoulders 44 and 45' are spaced equal distances from the stopportions 6' of the respective asso ciated pawls 4, so that the couplingshoulders 44 and 45' of the pawls 4 are staggered relative to eachother, respectively, distances e.

Each coupling lever 35 has a forked end with a slot in which a fulcrumpin 43 is located for supporting the coupling levers 35 for turningmovement, and also for movement in the longitudinal direction of therack 1. Fulcrum pin 43 is mounted on a rocking member 52 of U-shapedconfiguration, best seen in FIG. 1b. Rocking member 52 is mounted on astationary shaft 53 supported on frame wall 50 and is turnable togetherwith fulcrum pin 43. Springs 8 connect arms 9 of pawls 4 with rockingmember 52 so that the latter is biassed to turn in clockwise directionabout shaft 53 until shaft 43 abuts a stationary abutment surface 50"which is part of the frame 50 of the machine. One wall of the frame 50is shown in FIG; lb, and another wall 5-9 schematically indicated inhatched section, the walls 50 supporting a shaft 53. When a couplinglever 35 is displaced to the right, rocking member 52 is turned incounterclockwise direction against the action of spring 8 with fulcrumpin 43.

Actuating means are provided for coupling levers 35 and include springs42 connecting the coupling levers 35 with a holding portion 36 of adrive means 36 which has a sleeve 38 mounting drive means 36 for turningmovement on a stationary shaft 38. Springs 42 suspend the three couplinglevers 35 in engagement with fulcrum pin 43, but permit independentmovement of coupling levers 35. While springs 42 urge coupling levers 35into engagement with fulcrum pin 43, the stronger springs 8 acting onrocking member 52 and fulcrum pin 43, do not permit turning of rockingmember 52 by springs 42.

A stud 39 on arm 37 of drive means 36 abuts a stationary abutment 50' onthe frame of the machine under the action of springs 42. A back spacingmeans 41, connected to the back spacing key of the typewriter, notshown, embraces bolt 39, as also shown in FIG. 112, so that uponoperation of the back spacing key, arm 37 with drive means 36 is turnedin counterclockwise direction about shaft 38.

In the normal position of rest of drive means 36, illustrated in FIG.1a, its holding part 36' holds the coupling levers in a position of restin which one of the superimposed coupling portions 35' is locatedopposite the deep recess portion a between shoulders 45' and 45 of oneof pawls 4. When this coupling lever 35 is turned about fulcrum pin 43,its coupling portion 35' moves into the deep recess portion 45a untilabutting abutment 45 in the position of FIG. 4 which shows the threepawls 4 in the same position as FIG. 1a, and coupling portion 35 of therearmost coupling lever 35 between shoulders 45' and 45" of the shortestrearmost pawl 4 which has a stop portion 6' which is spaced twodistances 0 from the blocking shaft 7. Coupling portion 35' of theforemost coupling lever 35 is located opposite coupling shoulder 44 ofthe longest pawl 4, while coupling portion 35 of the intermediatecoupling lever 35 is spaced from coupling shoulder 44 of the associatedintermediate pawl 4.

Drive means 36 is turned by back spacing means 41 in counterclockwisedirection, and during such movement a transversely projecting drive part36" moves in forward direction, and a transversely projecting drive part36" moves in the rearward direction. Coupling members 35 have abutments35 and 35" respectively cooperating with the forwardly acting drive part36" and the rearwardly acting drive part 36". In the position of FIG.1a, in which coupling levers 35 are in the position of rest, abutments35" are all located opposite the rearwardly acting drive part 36",whereas abutments 35" are not located in the path of movement of theforwardly acting drive part 36". However, when coupling portion 35' ofone of the coupling levers 35, for example of the rearmost couplinglever 35 is moved into the deep recess portion 45a until abuttingabutment 45, as shown in FIG. 3a, the respective abutment 35" is locatedopposite the forwardly acting drive portion 36, while the abutment 35"is no longer located in the path of movement of the rearwardly actingdrive part 36".

FIG. 1a shows in its right portions a number of parts which have notbeen described since these parts belong to a carriage return device Rcooperating with the escapement mechanism P which are not objects of thepresent invention. All these parts are omitted for the sake of clarityin FIGS. 2a and 2b, which show the position of rest, and FIGS. 3a and 3bwhich show an operational position of the back spacing mechanism Saccording to the present invention.

FIG. 1a and FIG. 2a show a basic operational position in which all threeengaging portions 5 are located in the same recess between teeth 3' and3". FIGS. 3a and 3b show the mechanism in an operational position inwhich a back spacing step of the carriage for a distance 2 has beenaccomplished by operation of the back spacing means 41. For a betterunderstanding a system of parallel lines 34 indicates the spacing tbetween adjacent recesses, each distance r being the sum of threedistances e so that e is one-third of distance t.

In the position of FIGS. 2a and 2b, in which stop portion 6 of "theforemost pawl 4 abuts blocking means 7 and blocks carriage movement, theother two pawls 4 are held by the respective springs 8 in engagementwith the leading flank of tooth 3. Coupling portion 35' of the rearmostcoupling lever 35 is located opposite the deep recess portion 45a of therearmost pawl 4.

When back spacing means 41 is moved to the right, drive means 36 isturned in counterclockwise direction and holding portion 36' releasesall three coupling levers 35 so that coupling levers 35 are raised bysprings 42, and coupling portions 35' try to enter into the recesses inthe corresponding pawls 4. Coupling portion 35 of the rearmost couplinglever 35 enters the deep recess portion 45a of the respective rearmostpawl 4, abutting the coupling edge 45, while abutments 44 limit themovement of coupling portions 35 of the other two coupling levers 35.The rear edge of the foremost coupling portion 35' is located oppositethe foremost coupling shoulder 44' as best seen in FIG. 4.

Since the rearmost coupling lever 35 has moved to a higher position, itsabutment 35", see FIG. 3a, is located opposite the forwardly actingdrive part 36", while its abutment 35" is no longer located in the pathof movement of the rearwardly acting drive part 36- of drive means 36.

In this manner, a selective coupling between drive means 36 and pawls 4has been obtained, and when under the control of back spacing means 41,drive means 36 is further turned in counterclockwise direction, theforwardly acting drive part 36" moves through coupling means 35, 35 and45' the rearmost escapement pawl 4 from the trailing position shown inFIG. 2a to the leading position shown in FIG. 3a so that this pawl 4 hasmoved two distances e until its stop portion 6' abuts blocking shaft 7,as shown in FIG. 30.

At the same time, the rearwardly acting drive part 36" engages abutments35" of the two forward coupling levers 35 and shifts the same inrearward direction to the right as viewed in the drawing so that rockingmember 52 is displaced against the action of springs 8. Coupling portion35' of the foremost coupling lever 35 engages coupling shoulder 44 andmoves the foremost largest escapement pawl 4 back for about twodistances e so that rack 1 with the paper carriage is shifted back acorresponding distance in rearward direction, while the respective stopportion 6' moves away from blocking shaft 7.

While engaging portion of the rearmost pawl 4 moves forward toward theleft, it is urged by a flank of tooth 3" out of the recess between teeth3' and 3", and while the foremost pawl 4 moves the carriage in rearwarddirection, engaging portion 5 of the rearmost pawl 4 moves over tooth 3"and falls into the next following recess under the action of therespective spring 8. The shortest pawl 4 moves forward to lead the otherpawls 4 and stops the carriage movement when stop portion 6- abutsblocking shaft 7 in the position shown in FIGS. 3a and 3b.

When the back spacing means 41 are released, and drive means 36 isreturned by springs 42 in clockwise direction to the normal position ofrest shown in FIGS. 2a, 2b, the shortest rearmost pawl 4 is in theleading position abutting blocking means 7 and blocking carriagemovement. The position of the three pawls 4 is the same as if, startingfrom the position of FIG. 2a, a step of two distances e would have beenperformed in the forward writing direction, that is to the left asviewed in the drawing, the difference being that in this event tooth 3'would be in the position in which tooth 3" is in the position of FIG. 3awhich shows the corresponding position after a backward step.

The three possible relative positions of escapement pawls 4 are shown inFIGS. 4, 5 and 6. In the position of FIG. 5, the rearmost pawl 4 leadsthe other pawls 4, and in the position of FIG. 6, the middle pawl 4leads. In all relative positions of pawls 4, the deeper recess portion45a of a pawl 4 which trails the other two pawls 4 two distances 2, islocated opposite the coupling portion 35 of the respective couplinglever 35, so that this trailing pawl 4 is engaged at the couplingshoulder 45 and forwardly shifted to become the blocking pawl 4, whilethe previously blocking pawl 4 is engaged at the coupling shoulder 44'by the respective coupling lever 35 and shifted rearwards together withthe paper carriage. The respective third pawl 4, which trails theblocking pawl 4 only one distance e, follows the originally blockingpawl 4 which moves the carriage rearward due to its engagement with theteeth 3 of the rack 1, without any influence on the back spacingoperation.

FIGS. 4, 5 and 6 illustrate the coupling positions of coupling levers 35depending on the relative positions of the escapement pawls 4.

In the position of pawls 4 shown in FIGS. 2a and 4, the foremost pawl 4is the blocking pawl and is shifted rearward by coupling portion 35'engaging coupling shoulder 44 while the carriage is stopped by therearmost pawl 4 which is shifted in writing direction by couplingportion 35 engaging coupling shoulder 45 of the rearmost pawl 4.

In the pawl position shown in FIGS. 3a and 5, the rearmost blocking pawl4 is shifted backward by the rearmost coupling portion 35 which engagescoupling shoulder 44 of the respective pawl 4, while the carriage isstopped by the middle pawl 4 forwardly shifted by the intermediatecoupling portion 35' engaging coupling shoulder 45'.

In the position of FIG. 6, the middle pawl 4 is the blocking pawl and isshifted rearwardly by the respective coupling portion 35 which engagescoupling shoulder 44' while the carriage is stopped by the foremost pawl4 shifted in writing direction by coupling portion 35 engaging couplingshoulder 45.

In the illustrated embodiment, three pawls 4 are provided, and thesmallest step e is one-third of the spacing between adjacent rack teeth3. As explained above, a coupling lever 35 must move the blocking pawl 4in rearward direction, and the pawl 4 whose stop portion 6' trails thestop portion 6 of the leading blocking pawl 4 two distances e, must beforwardly moved in order to stop the movement of the carriage. Theremaining pawl 4 follows the motions without having any influence on thedisplacement of the carriage.

From the above description it will become apparent that a set ofcoupling means 35, is provided and that each coupling means 35, 35' canbe individually moved between a position of rest shown in FIG. 1a, afirst coupling position coupled with the leading pawl 4 which initiallyblocks carriage movement along the coupling shoulder 44', and a secondcoupling position coupled with the pawl 4 which trails the leading pawl4 two distances e by engaging its coupling shoulder 45. In the firstcoupling position, the rearwardly moving drive part 36 of drive means 36effects through the coupling means 35, 35' in the first couplingposition a back spacing movement of the leading pawl 4 and of thecarriage, while drive part 36 moves the trailing pawl 4, which iscoupled with the coupling means 35, 35 in the second coupling position,in writing direction.

What is claimed as new and desired to be secured by Letters Patent is:

1. Back spacing mechanism for a carriage which is movable forward andrearward in one direction and has a rack with teeth and recesses,comprising, in combination, a set of escapement pawls cooperating withsaid rack and having stop portions staggered relative to each other apredetermined distance in said one direction and being individuallymovable forward and rearward in said one direction and into and out ofsaid recesses; resilient means urging said pawls into said recesses;blocking means engaging said stop portion of the pawl leading in saidone direction for blocking forward movement of said carriage while saidstop portions of the other pawls are rearwardly spaced from the leadingstop portion and from said blocking means; a set of coupling meansrespectively correlated with said pawls, each coupling means beingmounted for movement in said one direction, and for individual movementbetween a position of rest, a first coupling position coupled with theleading pawl which engages said blocking means, and a second couplingposition coupled with another pawl whose stop ortion trails said leadingstop portion; actuating means for moving said set of coupling means tosaid first and second coupling positions, and for moving the couplingmeans in said first coupling position together with the leading pawlrearward so that said leading pawl moves said rack and said carriagerearward, and for moving the coupling means in said second couplingposition forward so that the respective other pawl moves out of anengaged recess and forward relative to the rearwardly moving rack, andthen engages the next leading recess of said rack while the stop portionthereof engages said blocking means for blocking forward movement ofsaid carriage; and back spacing means for operating said actuatingmeans.

2. Back spacing mechanism according to claim 1 wherein saidpredetermined distance is the distance between adjacent recesses of saidrack divided by the number of pawls in said set of escapement pawls;wherein said number of pawls is at least three; and wherein the couplingmeans in said second coupling position engages the pawl whose stopportion trails said leading top portion a distance equal to twice saidpredetermined distance.

3. Back spacing mechanism according to claim 1 wherein said actuatingmeans include biassing means for urging each of said coupling means intosaid first and second coupling positions and a drive means havingrearwardly and forwardly acting drive parts for respectively moving thecoupling means in said first coupling position backward, and thecoupling means in said second coupling position forward, said drivemeans having a normal position for holding said set of coupling means insaid position of rest and being movable to an actuating position forreleasing said set of coupling means for movement to said first andsecond coupling positions, and for moving said set of coupling means insaid first and second coupling positions in said one direction rearwardand forward, respectively, with the respective pawls; and wherein saidback spacing means moves said drive means to said actuating position.

4. Back spacing mechanism according to claim 1 wherein saidpredetermined distance is the distance between adjacent recesses of saidrack divided by the number of pawls in said set of escapement pawls;wherein said number of pawls is at least three; wherein the couplingmeans in said second coupling position engages the pawl whose stopportion trails said leading stop portion two of said predetermineddistances; wherein said actuating means include biassing means forurging said set of coupling"means into said first and second couplingpositions, and a drive means having rearwardly and forwardly actingdrive parts for respectively moving a coupling means in'said firstcoupling position rearward, and a cou pling means in said secondcoupling position forward, said drive means having a normal position forholding said setjaof coupling means in said position of rest and beingmovable to an actuating position for releasing said set of couplingmeans for movement to said first and second coupling positions, and formoving said set of coupling means in said first and second couplingpositions in said one direction rearward and forward, respectively, withtherespective pawls; and wherein said back spacing means moves saiddrive means to said actuating position. 1

5. Back spacing mechanism according to claim 4 wherein each of saidpawls has a coupling recess, each coupling recess having a firstcoupling shoulder and a second coupling shoulder and a shallower recessportion bounded by said first coupling shoulder and a deeper recessportion bounded by said second coupling shoulder, wherein jsaid firstand second coupling shoulders of each of said pawls are staggeredrelative to the corresponding coupling shoulders of the other pawls saidpredetermined distance; wherein said set of coupling means have couplingportions registering in said position of rest, one of said couplingportions being located opposite said deeper recess portion, and theother coupling portions being located opposite said shallower recessportions of the corresponding pawls, and one of said other couplingportions having a face aligned with said first coupling shoulder of therespective pawl so that upon movement of said drive means to saidactuating position, said one coupling portion enters said deeper recessportion and engages said second coupling edge of the respective pawl insaid second coupling position while said one of said other couplingportions engages said first coupling shoulder.

6. Back spacing mechanism according to claim 5 wherein each of said setof coupling means has first and second abutments respectivelycooperating with said rearward and forwardly acting drive parts, saidfirst abutments being located in the path of movement of said rearwardacting drive part in said position of rest and in said first couplingposition of said set of coupling means, and said second abutments beinglocated outside of the path of movement of said rearward acting drivepart in said position of rest and in said first coupling position, andin the path of movement of said forwardly acting drive part in saidsecond coupling position so that upon movement of said drive means tosaid actuating position, the coupling means in said second couplingposition shifts the trailingpawl to a leading position, while thecoupling means in said first coupling position shifts the leading pawltwice said predetermined distance rearward in said one direction.

7. Back spacing mechanism according to claim 6 wherein said set ofcoupling means are coupling levers; wherein said biassing means of saidactuating means include a set of springs respectively connecting saidcoupling levers with said drive means; and a support supporting saidcoupling levers for turning movement between said position of rest andsaid first and second coupling positions, and for movement in said onedirection together with the pawls coupled thereto.

8. Back spacing mechanism according to claim 7 wherein said support is arocking member mounted for angular movement; and wherein said resilientmeans include a set of springs respectively connecting said pawls withsaid rocking member and urging said pawls to move rearward in said onedirection and into said recesses of said rack.

9. A back spacing mechanism according to claim 8 wherein said blockingmeans is a stationary shaft; and wherein said pawls have slots extendingin said one direction and being closed at one end by said stop portions,respectively, said stop portions being semi-circular and havingsubstantially the same diameter as said stationary shaft; and whereinsaid stationary shaft is located in said slots for supporting said pawlsfor forward and rearward movement in said one direction, and for angularmovement into and out of said recesses of said rack; and wherein saidsemi-circular stop portion of the leading pawl slidingly abuts saidstationary shaft, and the other stop portions are spaced in multiples ofsaid predetermined distance rearward in said one direction from saidstationary shaft.

10. Back spacing mechanism according to claim 8 and including a shaftsupporting said drive means for turning movement between said positionof rest and said actuating position; and wherein said drive means has anarm with a projecting stud; and wherein said back spacing means has amember embracing said stud for turning said drive means; and comprisinga stationary stop engaged by said stud in said position of rest of saiddrive means.

11. A back spacing mechanism according to claim 1 wherein said blockingmeans is a stationary shaft; wherein said pawls have slots extending insaid one direction and being closed at one end by said stop portions;wherein said stop portions are semi-circular and have substantially thesame diameter as said stationary shaft; wherein said stationary shaft islocated in said slots and supports said pawls for forward and rearwardmovement in said one direction, and for angular movement into and out ofsaid recesses of said rack; wherein said resilient means urge said pawlsto move rearward in said one direction and to turn into said recesses;and wherein said carriage and rack are biased to urge said pawls againstthe action of said resilient means toward said stationary shaft so thatsaid semi-circular stop portion of said leading pawl abuts saidstationary shaft.

12. Back spacing mechanism according to claim 1 wherein said pawls haverecesses bounded by first and second coupling shoulders, said couplingshoulders of said pawls being staggered multiples of said predetermineddistance; wherein said sets of coupling means engage said first couplingshoulder of the respective pawl in said first coupling position, andsaid second coupling shoulder in said second coupling position; andwherein said actuating means include a set of biassing springsrespectively urging said set of coupling means into said first andsecond coupling positions, and drive means operated by said back spacingmeans to move the coupling means in said first coupling positionrearward in said one direction with the respective pawl, and thecoupling means in said second coupling position forward in said onedirection with the respective pawl.

13. Back spacing mechanism according to claim 12, wherein said biassingsprings connect said drive means with said set of coupling means,respectively; wherein said drive means is mounted for turning movementand is urged by said biassing springs to turn in one direction ofrotation; and including stop means for stopping turning movement of saiddrive means in a normal position in which said set of coupling means arein said position of rest.

14. Back spacing mechanism according to claim 1.

wherein said predetermined distance is the distance between adjacentrecesses of the rack divided by the number of pawls in said set ofescapement pawls; wherein said number of pawls is at least three;wherein said blocking means is a stationary shaft supporting said pawlsfor forward and rearward movement in said one direction, and

for angular movement into and out of said recesses; wherein saidstaggered stop portions cooperate with said stationary shaft forblocking carriage movement; wherein the coupling means in said firstcoupling position engages said leading pawl whose stop portion abutssaid stationary shaft, and the coupling means in said second couplingposition engages the pawl whose stop portion is located rearward of saidstationary shaft and of said stop portion of the leading pawl a distanceequal to twice said predetermined distance.

15. Back spacing mechanism according to claim 1 and including a rockingmember having a shaft supporting said set of coupling means for forwardand rearward movement and for independent turning movement between saidposition of rest and said first and second coupling positions; andwherein said resilient means include a set of springs respectivelyconnecting said pawls with said rocking member so that said pawls arebiassed to move rearward in said one direction and said set of couplingmeans are biassed to move forward in said one direction.

References Cited UNITED STATES PATENTS 2,547,449 4/1951 Dodge 197842,701,045 2/1955 Madsen 19791 2,753,973 7/1956 Dodge et al. 197-842,905,303 9/1959 Palmer et al. 19784 2,972,401 2/1961 Salto 197843,288,262 11/1966 Salto 197-9l X ERNEST T. WRIGHT, JR., Primary ExaminerUS. Cl. X.R. 197-84

